2.3HTTP Listener

The first component is the source of the flow.

Conceptually:

app.post("/customers", async (req, res) => {
    ...
});

In Mule XML you'll see something resembling:

<http:listener
    config-ref="HTTP_Listener_config"
    path="/customers"
    allowedMethods="POST"/>

The Listener configuration might be:

<http:listener-config name="HTTP_Listener_config">

    <http:listener-connection
        host="0.0.0.0"
        port="8081"/>

</http:listener-config>

So locally:

http://localhost:8081/customers

starts the flow.